From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754739AbcBVLJF (ORCPT ); Mon, 22 Feb 2016 06:09:05 -0500 Received: from mail-pf0-f180.google.com ([209.85.192.180]:34813 "EHLO mail-pf0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754687AbcBVLIZ (ORCPT ); Mon, 22 Feb 2016 06:08:25 -0500 From: SeongJae Park X-Google-Original-From: SeongJae Park Date: Mon, 22 Feb 2016 20:08:15 +0900 (KST) To: David Howells cc: SeongJae Park , Paul McKenney , Jonathan Corbet , linux-doc , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] Documentation/memory-barriers: fix wrong comment in example In-Reply-To: <26215.1456135273@warthog.procyon.org.uk> Message-ID: References: <1455948068-14221-1-git-send-email-sj38.park@gmail.com> <20160220195722.GG3522@linux.vnet.ibm.com> <20160221052542.GJ3522@linux.vnet.ibm.com> <26215.1456135273@warthog.procyon.org.uk> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 22 Feb 2016, David Howells wrote: > SeongJae Park wrote: > >> a = 0; >> /* Code that does not store to variable a. */ >> + does_not_change_a(); >> a = 0; > > Since it's not actually code that's meant to be executed, you could make it: > > a = 0; > ... code that does not store to variable a ... > a = 0; I selected Paul's third option because the function could be noop (In this case, it doesn't break the original meaning) and it makes the code looks complete. However, your suggestion looks much better than the comment, too. So, I am attaching a patch that applying your suggestion below. =============================== >3 ==================================== >>From f7b5677790771599f418f1d95536935be971ae86 Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Mon, 22 Feb 2016 19:26:18 +0900 Subject: [PATCH] Documentation/memory-barriers: polish compiler store omit example Comments of examples about compiler store omit in memory-barriers.txt is about code that could be possible at that point. However, someone could interpret the comment as an explanation about below line. This commit exploits the intent more explicitly by changing the comment to be seems like a possible code rather than explanation about below line. Signed-off-by: SeongJae Park --- Documentation/memory-barriers.txt | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 904ee42..dc66351 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1459,7 +1459,7 @@ of optimizations: the following: a = 0; - /* Code that does not store to variable a. */ + ... Code that does not store to variable a ... a = 0; The compiler sees that the value of variable 'a' is already zero, so @@ -1471,7 +1471,7 @@ of optimizations: wrong guess: WRITE_ONCE(a, 0); - /* Code that does not store to variable a. */ + ... Code that does not store to variable a ... WRITE_ONCE(a, 0); (*) The compiler is within its rights to reorder memory accesses unless -- 1.9.1 > > David >